There is considerable interest in encoding audio as well as video signals for various applications. For example, in order to identify what an individual or an audience is listening to at a particular time, a listener's environment is monitored for audio signals at regular intervals. If the audio signals contain an identification code, those audio signals may be identified by reading such a code.
It is known to encode an identification code in conjunction with a broadcast signal. For example, it is known to encode both a payload signal and an ancillary signal into an audio signal, where the ancillary signal includes an identification code. By detecting and decoding the ancillary code, and associating the detected code with one or more individuals, it is possible to correlate media audience activity to the delivery of a particular payload signal.